Structure, Heat Capacity, and High-Temperature Thermal Properties of Yb₁₄Mn_1−xAl_xSb₁₁

A series of compounds, Yb₁₄Mn_1−-xAl_xSb₁₁ with (0 < x < 1), was prepared via Sn flux and the structures investigated. Single-crystal X-ray diffraction reveals that the volume of the unit cell increases with increasing Al content. Bond-distance changes are less than 2% and the increase in volume of the unit cell is associated with the decreasing distortion of the tetrahedron with increasing Al content. The specific heat, C_p, was measured from 300 to 1100 K. The measured C_p for these compounds is 19% higher than the Dulong-Petit value at the peak zT temperature (1223 K). These measured values permit a recalculation of thermal conductivity, revealing an extremely low lattice thermal conductivity of approximately 0.3−0.4 W/(m K) at 1223 K. The maximum zT of Yb₁₄Mn_1−xAl_xSb₁₁ is approximately 0.8 and 1.1 for the x = 0 and x = 0.6 compositions, respectively.